1. Field of the Art
The present invention relates to a signal converting apparatus and method, particularly to a signal converting apparatus and method of efficiently processing the components of a luminance signal and a color signal and thereby, generating a higher-resolution picture signal.
2. Background Art
The standard telecast in Japan uses the NTSC system. Recently, however, a higher-quality telecast system represented by hi-vision is developed and gradually spread. In the case of the NTSC system, the number of scanning lines is set to 525 and the aspect ratio is set to 4:3. In the case of the hi-vision system, however, the number of scanning lines is set to 1,125 and the aspect ratio is set to 16:9. Therefore, when using the hi-vision system, it is possible to enjoy realistic pictures having higher resolution.
To display a picture according to the NTSC system on a television receiver according to the hi-vision system, it is necessary to convert an SD (Standard Definition) signal corresponding to a video signal according to the NTSC system into an HD (High Definition) signal corresponding to a higher-resolution video signal. Hereafter, a signal before converted into more number is properly referred to as an SD signal, SD data, or an SD pixel and a signal after converted into more number is referred to as an HD signal, HD data, or an HD pixel.
Conversion of the SD signal into the HD signal has been performed by simple interpolation in the horizontal direction and vertical direction.
However, because the interpolation is performed by a cascaded FIR filter, the resolution of an HD signal is the same as that of an original SD signal. When a normal picture is used as a conversion object, the resolution of an HD signal is inferior to that of an SD signal due to conversion loss in a static picture section because the vertical interpolation is performed through in-field processing but inter-field correlation is not used.
Therefore, the applicant proposed in Japanese Patent Application No. 6-205934 a system of performing class division in accordance with a three-dimensional (space-time) distribution at a picture signal level serving as an input signal and operating an optimum estimated value as an HD signal by using a predicted coefficient previously obtained through learning for each class.
However, though a high-resolution picture can be obtained by processing both luminance signal and color signal by the above proposed system, problems occur that the capacity of a ROM for storing coefficient increases, an apparatus increases in size and moreover, the cost increases.
The present invention is made to solve the above problems and provides a signal converting apparatus and a signal converting method making it possible to realize downsizing and cost saving.
To solve the above problems, in the present invention, a signal converting apparatus for converting a first digital picture signal into a second digital picture signal different from the first digital picture signal is provided with a converting circuit for converting the above first digital picture signal into a luminance signal component and a color signal component, a memory for storing a coefficient to convert the luminance signal component of the above first digital picture signal into a luminance component of the above second digital picture signal for each class, a class classification circuit for deciding a class from the luminance signal component of the above first digital picture signal; a first arithmetic circuit for reading a coefficient corresponding to a class decided by the above class classification circuit from the above memory, performing the product-sum-operation of the read coefficient and the luminance signal of the above first digital picture signal, and obtaining the luminance signal component of the above second digital picture signal, and a second arithmetic circuit for performing the product-sum-operation of a coefficient based on the physical relationship of the scanning lines of the above first digital picture signal and the above second digital picture signal, and the color signal component of the above first digital picture signal, and obtaining the color signal component of the above second digital picture signal.
Moreover, in the present invention, a signal converting method for converting a first digital picture signal into a second digital picture signal different from the first digital picture signal, converts a first digital picture signal into a luminance signal component and a color signal component, decides a class from the luminance signal component of the above first digital picture signal, reads out a coefficient corresponding to the above decided class to convert the luminance signal component of the above first digital picture signal into a luminance component of the above second digital picture signal read from a memory, and performs the product-sum-operation of the read coefficient and the luminance component of the above first digital picture signal to obtain the luminance signal component of the above second digital picture signal, and performs the product-sum-operation of a coefficient based on the physical relationship of the scanning lines of the above first digital picture signal and the above second digital picture signal and the color signal component of the above first digital picture signal to obtain the color signal component of the above second digital picture signal.